This invention concerns a two-fluid nozzle which is adjustable to provide a substantially constant mixing energy. This invention also concerns an improved process for the partial oxidation of a carbonaceous slurry to produce a H.sub.2 and CO containing product gas.
Two-fluid nozzles, also called gas-atomizing nozzles or pneumatic nozzles, break up a stream of liquid by contacting it with a high velocity stream of gas, usually air or steam. The degree of break-up, i.e., atomization, of the liquid has been found to be directly related to the mixing energy provided by the nozzle. Mixing energy is defined as either the isothermic or adiabatic gas expansion energy per unit mass of liquid being atomized and is partially dependent upon the pressure drop across the nozzle. In application, the nozzle is dimensioned and configured to provide the required pressure drop to achieve the desired mixing energy, given the gas identity, mass flow rate and temperature of the gas and the mass flow rate of the liquid. So long as the above variables affecting mixing energy remain constant, the nozzle will produce the atomization required. This constancy in atomization is very important in spray drying as liquid particle size must be specified and uniform to produce the desired product. Constant uniform atomization is also very important when the atomizer is acting to feed a reaction vessel, such as a coal gasifier. Coal gasification by non-catalytic partial oxidation of a carbonaceous slurry needs uniform atomization to insure proper burn, to prevent hot spots in the reaction zone and to achieve process efficiency.
It is recognized that maintenance of atomizer dimension and configuration is especially difficult when the liquid to be atomized contains solids, such as would be the case in coal gasification where the liquid is a slurry comprised, for example, of water and ground coal. These solids can erode the nozzle to such an extent that its pressure drop design is lost. With a change in pressure drop, there is a concomitant change in mixing energy thereby altering the degree of atomization. Reestablishing the desired atomization criteria generally entails shutting down the process and replacing the nozzle. This can be very expensive, especially if the reaction zone must be depressurized and cooled down to achieve nozzle replacement.
It is therefore an object of this invention to provide a two-fluid nozzle and process therefor which yields uniform atomization through maintaining substantially constant mixing energy during continuance of the served process, e.g., spray drying, partial oxidation, and the like.